Mold for injection molding preform with undercut lip

Abstract

The present invention provides an injection mold having an injection core mold for defining the inner wall of a lip portion in a preform having an undercut, a first lip cavity mold for defining the outer wall of the lip portion having no undercut, and a second lip cavity mold for defining the outer wall of the lip portion having the undercut. In the initial release after the injection molding process of the preform, the second lip cavity mold is first moved upwardly to secure a space wherein there is no obstruction around the outer periphery of the undercut. Thereafter, the injection core mold is upwardly moved such that the second injection core mold can be forcedly released from the molded preform while resiliently deforming the undercut in the outward direction, utilizing the space so formed. The barrel portion of the preform so molded is biaxially stretched to provide a so-called roll-on type biaxially oriented vessel having a ball received in the lip portion thereof.

I claim: 
     
       1. An injection mold for injection molding a preform having a cylindrical closed-end barrel portion and a lip portion formed on said barrel portion at an open end thereof, the lip portion including an undercut formed to extend inwardly, proceeding in a direction toward the open end of the barrel portion, said injection mold comprising: an injection core mold having an outer surface defining inner walls of said lip and barrel portions, said injection core mold being movable along a longitudinal axis relative to said preform;   an injection cavity mold having a cavity surface defining an outer wall of said barrel portion, said injection cavity mold being movable along the longitudinal axis relative to said preform;   a first lip cavity mold positioned adjacent to said injection cavity mold on mold closure and having a cavity surface defining an outer wall of a non-undercut area of said lip portion, said first lip cavity mold including a pair of lip cavity mold halves movable toward and away from each other in a transverse direction;   a second lip cavity mold positioned adjacent to said first lip cavity mold on mold closure and having a cavity surface defining an outer wall of the undercut of said lip portion, said second lip cavity mold being movable along the longitudinal axis relative to said preform;   a mold driving mechanism comprising means for effecting an initial release movement of said second lip cavity mold relative to the preform in the longitudinal direction by an initial amount of movement required to secure a space around said undercut area and means for thereafter causing said injection core mold to move relative to said preform in the longitudinal direction while resiliently deforming said undercut area outwardly;   wherein said injection core mold includes a core pin for defining the inner walls of said lip and barrel portions and a proximal end portion having an external diameter larger than that of said core pin, and wherein said second lip cavity mold includes a cylindrical portion surrounding a portion of said proximal end portion and having an inner bottom wall formed therein at a position opposite to the proximal end portion of said injection core mold and wherein said mold driving mechanism includes means for driving said second lip cavity mold in the direction of said longitudinal axis; and   wherein a side wall of the cylindrical portion of said second lip cavity mold includes an inner stepped wall formed therein to engage the proximal end portion of said injection core mold after said initial release movement and wherein a spring is disposed between said proximal end portion and said inner bottom wall.   
     
     
       2. An injection mold for injection molding a preform having a cylindrical closed-end barrel portion and a lip portion formed in said barrel portion at the open end thereof, the lip portion including an undercut formed to extend inwardly proceeding in a direction toward the open end of the barrel portion, said injection mold comprising: an injection core mold having an outer surface defining the inner walls of said lip and barrel portions, said injection core mold being movable along a longitudinal axis relative to said preform;   an injection cavity mold having a cavity surface defining the outer wall of said barrel portion, said injection cavity mold being movable along the longitudinal axis relative to said preform;   a first lip cavity mold positioned adjacent to said injection cavity mold on mold closure and having a cavity surface defining an outer wall of a non-undercut area of said lip portion, said first lip cavity mold including a pair of lip cavity mold halves movable toward and away from each other in a transverse direction;   a second lip cavity mold positioned adjacent to said first lip cavity mold on mold closure and having a cavity surface defining an outer wall of the undercut area of said lip portion, said second lip cavity mold being movable along the longitudinal axis relative to said preform;   a mold driving mechanism comprising means for effecting an initial release movement of said second lip cavity mold relative to the preform in the longitudinal direction by an initial amount of movement required to secure a space around said undercut area and means for thereafter causing said injection core mold to move relative to said preform in the longitudinal direction while resiliently deforming said undercut area outwardly;   wherein said injection core mold includes a core pin for defining the inner walls of said lip and barrel portions and a proximal end portion having an external diameter larger than that of said core pin, and wherein said second lip cavity mold includes a cylindrical portion surrounding a portion of said proximal end portion and having an inner bottom wall formed therein at a position opposite to the proximal end portion of said injection core mold, and wherein said mold driving mechanism includes means for driving said second lip cavity mold in the direction of said longitudinal axis; and   an actuator located between said proximal end portion and said inner bottom wall for transmitting the driving force from said second lip cavity mold to said injection core mold after said initial movement, but not transmitting the driving force from said second lip cavity mold to said injection core mold during said initial movement.   
     
     
       3. An injection mold for injection molding a preform having a cylindrical closed-end barrel portion and a lip portion formed in said barrel portion at the open end thereof, the lip portion including an undercut formed to extend inwardly proceeding in a direction toward the open end of the barrel portion, said injection mold comprising: an injection core mold having an outer surface defining the inner walls of said lip and barrel portions, said injection core mold being movable along a longitudinal axis relative to said preform;   an injection cavity mold having a cavity surface defining the outer wall of said barrel portion, said injection cavity mold being movable along the longitudinal axis relative to said preform;   a first lip cavity mold positioned adjacent to said injection cavity mold on mold closure and having a cavity surface defining an outer wall of a non-undercut area of said lip portion, said first lip cavity mold including a pair of lip cavity mold halves movable toward and away from each other in a transverse direction;   a second lip cavity mold positioned adjacent to said first lip cavity mold on mold closure and having a cavity surface defining an outer wall of the undercut area of said lip portion, said second lip cavity mold being movable along the longitudinal axis relative to said preform;   a mold driving mechanism comprising means for effecting an initial release movement of said second lip cavity mold relative to the preform in the longitudinal direction by an initial amount of movement required to secure a space around said undercut area and means for thereafter causing said injection core mold to move relative to said preform in the longitudinal direction while resiliently deforming said undercut area outwardly;   wherein said injection core mold comprises a first injection core mold section movable relative to said preform in the direction of the longitudinal axis, said first injection core mold section having a core pin for defining the inner wall of said barrel portion and a second injection core mold section through which said core pin passes, said second injection core mold section being movable relative to said preform in the direction of the longitudinal axis and having a surface for defining the inner wall of said lip portion and wherein said mold driving mechanism is adapted to drive said first injection core mold section and said second lip cavity mold as a unit in the direction of the longitudinal axis, whereby said second injection core mold section can be released and moved together with said first injection core mold section and said second lip cavity mold as a unit after the initial release movement in which said first injection core mold section is moved together with said second lip cavity mold as a unit;   wherein said first injection core mold section includes a proximal end portion at a proximal end of said core pin and having an external diameter larger than that of said core pin; and   wherein said second section of the injection core mold has a flange positioned to be engaged by said proximal end portion of said first section of the injection core mold, the second lip mold cavity includes a cylindrical portion having an inner wall, the inner wall of said cylindrical portion of said second lip cavity mold includes an inner stepped wall positioned to engage the flange portion of said second injection core mold section after said initial release movement and wherein a spring is disposed between said flange and an inner bottom wall of said cylindrical portion.   
     
     
       4. An injection mold for injection molding a preform having a cylindrical closed-end barrel portion and a lip portion formed in said barrel portion at the open end thereof, the lip portion including an undercut formed to extend inwardly proceeding in a direction toward the open end of the barrel portion, said injection mold comprising: an injection core mold having an outer surface defining the inner walls of said lip and barrel portions, said injection core mold being movable along a longitudinal axis relative to said preform;   an injection cavity mold having a cavity surface defining the outer wall of said barrel portion, said injection cavity mold being movable along the longitudinal axis relative to said preform;   a first lip cavity mold positioned adjacent to said injection cavity mold on mold closure and having a cavity surface defining an outer wall of a non-undercut area of said lip portion, said first lip cavity mold including a pair of lip cavity mold halves movable toward and away from each other in a transverse direction;   a second lip cavity mold positioned adjacent to said first lip cavity mold on mold closure and having a cavity surface defining an outer wall of the undercut area of said lip portion, said second lip cavity mold being movable along the longitudinal axis relative to said preform;   a mold driving mechanism comprising means for effecting an initial release movement of said second lip cavity mold relative to the preform in the longitudinal direction by an initial amount of movement required to secure a space around said undercut area and means for thereafter causing said injection core mold to move relative to said preform in the longitudinal direction while resiliently deforming said undercut area outwardly;   wherein said injection core mold comprises a first injection core mold section movable relative to said preform in the direction of the longitudinal axis, said first injection core mold section having a core pin for defining the inner wall of said barrel portion and a second injection core mold section through which said core pin passes, said second injection core mold section being movable relative to said preform in the direction of the longitudinal axis and having a surface for defining the inner wall of said lip portion and wherein said mold driving mechanism is adapted to drive said first injection core mold section and said second lip cavity mold as a unit in the direction of the longitudinal axis, wherein said second injection core mold section can be released and moved together with said first injection core mold section and said second lip cavity mold as a unit after the initial release movement in which said first injection core mold section is moved together with said second lip cavity mold as a unit;   wherein said first injection core mold section includes a proximal end portion at a proximal end of said core pin and having an external diameter larger than that of said core pin; and   wherein said second section of the injection core mold has a flange, the second lip mold cavity includes a cylindrical portion having an inner bottom wall at a position opposite to said flange portion of said second injection core mold section, said mold driving mechanism, further comprises: an actuator located between said flange portion of the second injection core mold section and said inner bottom wall for transmitting the driving force from said second lip cavity mold to said second injection core mold section after said initial release movement, but not transmitting the driving force from said second lip cavity mold to said second injection core mold section during said initial release movement.